Taters Versus Sliders: Evidence for A

Member Recognition Issue

VOL. 31, NO. 7 | J U LY 2 021

’Taters versus Sliders: Evidence for a Long-Lived History of Strike-Slip Displacement along the Canadian Arctic Transform System (CATS) ’Taters versus Sliders: Evidence for a Long- Lived History of Strike-Slip Displacement along the Canadian Arctic Transform System (CATS)

William C. McClelland, Dept. of Earth & Environmental Sciences, University of Iowa, Iowa City, Iowa 52242, USA; Justin V. Strauss, Dept. of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA; Maurice Colpron, Yukon Geological Survey, Whitehorse, Yukon Y1A 2C6, Canada; Jane A. Gilotti, Dept. of Earth & Environmental Sciences, University of Iowa, Iowa City, Iowa 52242, USA; Karol Faehnrich, Dept. of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA; Shawn J. Malone, Dept. of Geoscience, University of Wisconsin, Green Bay, Wisconsin 54311, USA; George E. Gehrels, Dept. of Geosciences, University of Arizona, Tucson, Arizona 85721, USA; Francis A. Macdonald, Earth Science Dept., University of California, Santa Barbara, California 93106, USA; John S. Oldow, Borealis, 200 E. Troxell Road, Oak Harbor, Washington 98277, USA, and Dept. of Geology, Western Washington University, Bellingham, Washington 98225, USA

ABSTRACT the northwestern Alaskan and Canadian followed mafic magmatism associated with Recent field-based studies indicate that the Arctic margins provide the clearest rationale the Franklin Large Igneous Province at 720 northern margin of North America is best for the rotation model (Embry, 1990), which Ma (Macdonald et al., 2010; Cox et al., interpreted as a tectonic boundary that experi- is by far the most commonly expressed 2015). The basin is flanked to the north by enced a long, complex history of strike-slip mechanism (e.g., Hutchinson et al., 2017; Ordovician to Silurian clastic and subduction- displacement. Structures juxtaposing the Miller et al., 2018). In contrast, we explore related mafic and ultramafic rocks and alloch- Pearya and Arctic Alaska terranes with North the implications of a growing set of onshore thonous units of the Pearya terrane (Fig. 1; America are linked and define the Canadian observations that indicate that the northern Trettin, 1998). The Pearya terrane is domi- Arctic transform system (CATS) that accom- Laurentian margin has experienced a pro- nated by two assemblages juxtaposed in modated Paleozoic terrane translation, trun- tracted history of translation. This view is the Ordovician: a displaced peri-Laurentian cation of the Caledonian orogen, and shorten- bolstered by a variety of data that support crustal fragment that records early Neo- ing within the transpressional Ellesmerian models of Paleozoic large-magnitude terrane proterozoic (Tonian) and Ordovician conver- orogen. The structure was reactivated during translation through the Arctic region (Colpron gent margin magmatism (Malone et al., 2017, Mesozoic translational opening of the Canada and Nelson, 2009). Despite early calls for 2019) and a latest Neoproterozoic (Ediacaran) Basin. Land-based evidence supporting trans- large-magnitude sinistral offsets (e.g., Boreal to Ordovician mafic arc complex built on lation along the Canadian Arctic margin is fault of Bally in Kerr et al., 1982; Canadian Tonian basement (Majka et al., 2021). Steeply consistent with transform structures defined transcurrent fault of Hubbard et al., 1987; dipping faults juxtaposed Pearya with the by marine geophysical data, thereby provid- Porcupine fault of Oldow et al., 1989), the Laurentian passive margin by the Devonian ing a robust alternative to the current consen- Canadian Arctic margin generally has not (Trettin, 1998; Malone et al., 2019). Sub- sus model for rotational opening of the been viewed as a viable candidate for trans- sequently, units of both the Pearya terrane Canada Basin. form boundaries to accommodate evolution and Franklinian basin were deformed within of the Arctic region (e.g., Doré et al., 2016). the Devonian–Carboniferous Ellesmerian INTRODUCTION Results of our recent field studies on the fold belt and overlain by Carboniferous and Recent ocean- and land-based studies of northern margin of Laurentia challenge this younger deposits of the Sverdrup basin. the circum-Arctic region bring significant conclusion and support translation. Structures of the Ellesmerian fold belt extend advances in high-quality data to formulate westward to Prince Patrick Island where they, new models for the tectonic evolution of the CURRENT SETTING and Carboniferous to Mesozoic structures of Arctic margin (e.g., Pease and Coakley, 2018; The Canadian Arctic Islands expose a the Sverdrup basin, are truncated at a high Piskarev et al., 2019; Piepjohn et al., 2019). south to north transition from shallow marine angle by the present-day Arctic margin (Fig. Nevertheless, evolution of the Canada Basin deposits of the Paleozoic Arctic platform into 1; Harrison and Brent, 2005). remains one of the most enigmatic and con- deep-water rocks of the late Proterozoic to Autochthonous strata of the Laurentian tentious topics of the Arctic. Two end-mem- early Paleozoic Franklinian basin that were margin in northern Yukon are juxtaposed ber models for the Mesozoic opening of the deformed in the Devonian and overlain by late with peri-Laurentian platform and basinal Canada Basin invoke Arctic Alaska (1) rift- Paleozoic and early Mesozoic rocks of the strata of the North Slope subterrane of Arctic ing and rotating (’taters) from or (2) translat- Sverdrup basin. Rocks of the Franklinian Alaska (Macdonald et al., 2009; Strauss et al., ing (sliders) along the Canadian Arctic basin were deposited after the Neoproterozoic 2019a, 2019b; Colpron et al., 2019) on a near- margin (Fig. 1 inset). Late Paleozoic and breakup of Rodinia and rifting along the vertical fault zone broadly referred to as the Mesozoic stratigraphic correlations between northern Laurentian margin, which closely Porcupine shear zone (Fig. 1; von Gosen et al.,

GSA Today, v. 31, https://doi.org/10.1130/GSATG500A.1. CC-BY-NC.

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Basin s Southwestern Brook Lomonoso Paleogene Gak Aleutia subterranes Chukchi Borderland fault FarewelFarewelll Amerasian Basin kel

n Makarov Paleozoic v Denali Kaltag fault R Rang Basin id Rid ge 150°W Canada 30°E T ge rench e Eurasian Basin area of inferred oceanic crust 30°W Svalbard Porcupin Alpha NorthNorth SlopSlSlopeopee Amerasia e Basin Ridge subterranesubterran e Harder Fjord Alaska Yukon e South ansform System de Geer Pacific Ridg Canadian Arctic Transform System St Elias Tuk nana north a Pearya Atlantic Ocean T Prince Patrick Island Banks Caledo r Yukon-Tanana north Island Sverdrup T Prince of BC basin Franklinian Ocean 0° NW Wales a Basin Charlotte nana south Devonian n ian Germania Land clastic wedge e AlexanderAlexande Tintin deformation zone kon-Tanana south 1 2 deformationdefo Queen Yu land EllesmerIslandIs Mtns Nunavut Mackenzie r W Greenland mati 0° Storstrømmen BanksBanks 9 Island on shear zone n ont frontfronfr t 120°120°WW n Arctic Alaska terraneBaffin 0500 fronfr pole of Bay o CordilleranCordillera Insular-Arctic terranes n rotation N t 60°W km 60°W 60° W deformationdeformatio 70°N70°N

Figure 1. Generalized terrane map showing the location of the Canadian Arctic transform system, geophysically defined features in the Canada Basin, and terrane distribution on the Arctic and Cordilleran margins of Laurentia (modified after Colpron et al., 2019). Insets show simplified (1) rotation and (2) translation models (from Patrick and McClelland, 1995).

2019). The North Slope subterrane was incor- Structures that accommodated translation the Porcupine shear zone while it was an porated into the greater Arctic Alaska terrane of Pearya project eastward to faults with active lithosphere-scale transform (Ward et and juxtaposed with the Laurentian margin similar timing and kinematics in Svalbard al., 2019). Strike-slip basin sedimentation by the Carboniferous (Strauss et al., 2013). (Fig. 1; Mazur et al., 2009). Although com- may be recorded by the newly recognized South-directed Late Devonian–Carboniferous monly linked with strike-slip faults in the Devonian–Carboniferous Darcy Creek for- structures on the north side of this boundary Caledonides (e.g., Storstrømmen shear zone; mation within the Porcupine shear zone mark the probable offset western continuation Fig. 1), we suggest that faults in Svalbard (Faehnrich et al., 2021). of the Ellesmerian orogen (Oldow et al., 1987). truncate the Caledonian structures and con- Linking strike-slip structures across tinue eastward to Scandinavia as the de Geer Svalbard and northern Ellesmere Island to PALEOZOIC TERRANE ACCRETION transform (Fig. 1; Lundin and Doré, 2019). Yukon and Alaska on the basis of orienta- AND TRANSLATION ON THE PEARYA The Harder Fjord fault zone, a long-lived tion, timing, and kinematics defines a AND PORCUPINE SHEAR ZONES steep structure that juxtaposes Ediacaran arc throughgoing Paleozoic fault system on the Models that invoke terrane translation from rocks with the Franklinian margin on North northern Laurentian margin (Fig. 1), referred the Arctic domain to the Cordilleran margin Greenland (Rosa et al., 2016), is similar to to here as the Canadian Arctic margin (e.g., Northwest Passage model; Colpron and faults in Pearya and Svalbard (Fig. 1). transform system (CATS). Recognition of Nelson, 2009) require a transcurrent bound- Strike-slip faults project westward from CATS carries significant implications for ary along the Paleozoic Arctic margin. Pearya to the boundary between the Paleozoic paleogeographic reconstructions Evidence for such a boundary on Ellesmere Laurentian margin and North Slope subter- of the northern Laurentian margin. Dis- Island was outlined by Trettin (1998) in his rane in Yukon (Fig. 1). This boundary is placement and terrane juxtaposition along assessment of the history of Pearya. Recent marked by the Porcupine shear zone, a broad the margin culminated with south-directed fieldwork has confirmed that Pearya is sepa- fault zone (>17 km wide) of older sinistral shortening of the Late Devonian–Early rated from the Laurentian margin by vertical and recent (late Cenozoic) dextral brittle Carboniferous Ellesmerian orogeny and strike-slip structures that record a complex deformation (von Gosen et al., 2019). The development of a thick clastic wedge derived history of reactivation, overprinting, and lithology and structural history of the North from a continental sediment source to the reversals in displacement direction (Piepjohn Slope subterrane contrast sharply with the north. The nature of this northern source et al., 2015). Current timing estimates for adjacent Laurentian margin rocks and are remains tentative but is most probably Paleozoic sinistral displacement suggest a more akin to units in northeastern Laurentia derived from the Arctic Alaska–Chukotka long-lived Ordovician to Devonian metamor- (Macdonald et al., 2009; Strauss et al., 2013; terrane (Beranek et al., 2010; Anfinson et phic and deformation history associated with Gibson et al., 2021). Although originally al., 2012). The CATS model that accommo- juxtaposition and translation of Pearya along interpreted to crosscut the shear zone (Lane, dates large-magnitude translational motion the Laurentian margin (McClelland et al., 1992), Devonian granitoids common to the of terranes suggests the source may have 2012; Kośmińska et al., 2019). North Slope subterrane were emplaced within varied through time.

www.geosociety.org/gsatoday 5 GRAINS AND TERRANES: WHERE The terranes of Svalbard, Pearya, and Laurentian signature of the North Slope sub- DID THEY COME FROM? North Slope show clear evidence of terrane and Franklinian basin. Terranes with Evidence for terrane displacement along Mesoproterozoic and older material consis- this signature are assigned origins adjacent the Arctic margin can be evaluated by com- tent with derivation from Laurentia but dis- to Baltica or Siberia (e.g., Beranek et al., paring detrital zircon data from the Paleozoic tinct from passive margin units in the 2013; White et al., 2016), consistent with fau- passive margin to terranes thought to have Franklinian basin. The Precambrian signa- nal (Soja and Antoshkina, 1997) and paleo- moved along it. Critical components include ture of the North Slope subterrane is most magnetic (Bazard et al., 1995) data. (1) variation in detrital zircon signatures compatible with northeastern Laurentia Ordovician to Silurian arc magmatism across northern Laurentia; (2) the ca. 970 Ma (Greenland), making a strong case for large- observed in the Arctic terranes indicates signature of the convergent margin external scale translation of a peri-Laurentian frag- that they largely represent displaced arc to Rodinia; (3) Neoproterozoic magmatic ment along the Arctic margin (Gibson et al., fragments. The age of individual peaks var- ages; and (4) Ordovician, Silurian, and 2021). The Tonian (ca. 970 Ma) signature of ies by terrane, and Hf isotopes range from

Devonian arc magmatism common to many the Pearya, Svalbard, Arctic Alaska, and juvenile (>+5 ɛHft) to evolved (<–5 ɛHft) of the displaced terranes. Tracking detrital Farewell terranes clearly distinguishes these settings (Fig. 2B), tracking differences in zircons in combination with their Hf isotopic crustal fragments from the Franklinian mar- arc basement and proximity to active con- signatures demonstrates significant differ- gin (Fig. 2). The Tonian signature is subtle to vergent boundaries. For example, Ordovician ences in provenance history between Arctic absent in the Alexander and Yukon-Tanana signatures are dominant in the Pearya, terranes and the Laurentian margin. For terranes, making it a useful discriminant as Alexander, Farewell, and Arctic Alaska ter- example, Proterozoic to Devonian units of well. Evidence for Neoproterozoic–early ranes, but lacking in Svalbard and portions Svalbard remain similar throughout their Paleozoic (710–520 Ma) magmatism coeval of the Yukon-Tanana terrane. Silurian mag- evolution, whereas Proterozoic to Silurian with activity in the Timanide orogen of east- matic rocks are absent from Pearya and the components of the Alexander terrane are ern Baltica (Fig. 3) appears in the Pearya, North Slope subterrane although both regions highly variable but coalesce to a common Arctic Alaska, Farewell, and Alexander ter- record influx of Silurian detrital compo- signature in the Devonian (Fig. 2A). ranes, but is notably missing from the nents. The εHft signatures for Ordovician and

20 A Precambrian input B Paleozoic input 15 Depleted Mantle Array

-0.4 SS ATn P3 (DM) P Sv SS F Ordovician Silurian Sv SS P 10 Sv CWp ATb ATb F F ATs P F D 5 .0 CW

N D t P ATn ATb WMA Chondritic Uniform N YTs 0 N εH f ATn Reservoir

Dim 2 ATb (CHUR) ATs -5 YTs 0. 40 FB -10

Paleoproterozoic Neoproterozoic Paleoproterozoic FB ATs -15

-0.4 0.0 Dim 1 0.4 Depositional Age εHf -20 ATs Sv N ATn P SS Devonian-Carboniferous > +5 ATb F D Silurian +5 to -5 -25 Ordovician < -5 Devonian Silurian Ordovician Proterozoic-Cambrian no data -30 340 350 360370 380 390 400 410420 430440 450460 470 480 490 500 Age(Ma)

Figure 2. (A) Two-dimensional multidimensional scaling (MDS) plot (Saylor et al., 2017; Kolmogorov-Smirnov comparison of probability density plots, metric squared test = 0.137) and (B) age-εHft plot of detrital zircon data from units involved in translation along the Canadian Arctic transform system. Annotations on (A) show general detrital age trends reflected in the MDS plot. Alexander terrane data in (B) is plotted as contoured density maps of bivariate kernel density estimates with contours of 68% (1σ) and 95% (2σ) of peak density and cool to hot color gradient reflecting increasing peak density (Sundell et al., 2019). Data from Svalbard (Sv); Franklinian basin (FB); Pearya terrane (P; P3—Succession 3); Canadian Arctic Islands clastic wedge (CW; CWp—Parry Islands Formation); Arctic Alaska terrane (N—North Slope subterrane; SS—southwestern subterranes; D—Doonerak; WMA—Whale Mountain Allochthon); Farewell terrane (F); Alexander terrane (AT: ATn—northern, St. Elias; ATs—southern, Prince of Wales Island; ATb—Banks Island assemblage); the Yukon-Tanana terrane (YTs) in southeastern Alaska is presented in additional plots and references in the supplemental material1.

1Supplemental Material. Probability plots, Shepard plot, and sources of U/Pb data in Figure 2A. Go to https://doi.org/10.1130/GSAT.S.14442635 to access the supplemental material; contact [email protected] with any questions.

6 GSA Today | July 2021 ~370 Ma SIBERISIBERIAA subterrane along the Laurentian continental Figure 3. Schematic Devo- margin, with the rest of Arctic Alaska and W F nian paleogeographic recon- N AT struction showing terrane Alexander located farther outboard. Final 30° Ch Timanidesd D Sv translation on the Canadian PALEO-PACIFIC YTs SS contraction in the northern Caledonides, rep- N Arctic transform system OCEAN resented by ultrahigh-pressure metamor- CATS P Caledonides BALTICA (CATS). Modified after Torsvik incipient YTn and Cocks (2017). AT—Alex- subduction phism at 360 Ma in North-East Greenland, STS ander terrane; Ch—Chukotka; D—Doonerak arc; F—Fare- was accompanied by sinistral and dextral 0° S-K well; N—North Slope sub- PROTO-TETHYS translation that accommodated margin- terrane; P—Pearya terrane; OCEAN LAURENTIA S-K—Sierra-Klamath ter- parallel escape from the orogen (Gilotti and ranes; SS—southwestern McClelland, 2007). This intra-Caledonian Arctic Alaska subterranes; strike-slip system was truncated by the 30°S ST—Stikinia; Sv—Svalbard; GONDWANAANA W—Wrangellia; YTn—Yukon- CATS, effectively transferring Caledonian Tanana terrane in Yukon; rocks of Svalbard to the Arctic margin ~1000 km RHEIC OCEAN YTs—Yukon-Tanana terrane in southeastern Alaska. (Fig. 3). The eastern continuation of CATS orogenic belt subduction zone transform ridge projects toward the truncated margin of northern Scandinavia marked by the Trollfjord-Komagelva fault system, requir- Silurian zircon in most terranes, ranging PALEOZOIC EVOLUTION OF THE ing an Ordovician–Devonian strike-slip from +5 to –15, record evolution in settings NORTHERN LAURENTIAN MARGIN history on this or an outboard structure along with variable input from older continental The variations in zircon age and εHft sig- the Timanide-Baltica suture. sources, either from the arc basement or natures in circum-Arctic and Cordilleran The amalgamated terranes translated influx of continentally derived sedimentary terranes record changes in Paleozoic arc along the Arctic margin shed detritus with material. In stark contrast, the southern magmatism that broadly represent a north- characteristic juvenile isotopic signatures Alexander terrane on Prince of Wales Island, ern continuation of the arc system associated (e.g., Anfinson et al., 2012) southward into along with the Doonerak arc and Whale with closure of Iapetus and the subsequent the Canadian Arctic Island clastic wedge Mountain allochthon of Arctic Alaska, con- Silurian collision of Baltica with Laurentia (Fig. 1). Middle Devonian arc magmatism sistently have a juvenile signature that indi- (Fig. 3; Strauss et al., 2017). These arc com- developed in Arctic Alaska simultaneously cates evolution in an intraoceanic setting iso- plexes are best viewed as age equivalent to with clastic wedge deposition. This activity lated from any continental input throughout subduction-related rocks preserved in the was contemporaneous with Uralian arc mag- their pre-Devonian history (Fig. 2). thrust sheets of the Caledonides. Svalbard matism on the Baltican margin, but the two Devonian–Carboniferous detrital zircon represents a Caledonian signature; however, systems were separated by the CATS. The signatures define amalgamation of terranes the other circum-Arctic terranes are arc Late Devonian marks a transition to subduc- and juxtaposition with the Arctic margin. The complexes that extended beyond the tion initiation along the western margin of Devonian clastic wedge in the Canadian Caledonides and are characterized by a mix- Laurentia with granitic magmatism present Arctic Islands records deposition on Laurentia ture of juvenile intraoceanic fragments (e.g., in the North Slope subterrane to the north from a more juvenile source emplaced along southern Alexander terrane, Doonerak) and and Yukon-Tanana, Stikinia, Quesnellia, the Franklinian margin (Patchett et al., 1999). arc fragments with continental substrates Kootenay, and Sierra-Klamath terranes to Late Devonian units (e.g., Parry Islands (e.g., Pearya, northern Alexander terrane). the south (Fig. 3). The CATS effectively Formation) at the top of the wedge are domi- Translation associated with the CATS initi- accommodated migration of Paleozoic arcs nated by Neoproterozoic to Devonian grains ated as Ordovician and Silurian subduction active outboard of the Laurentian margin with juvenile εHft (Anfinson et al., 2012). This migrated along the northern Laurentian mar- into the paleo-Pacific realm. Latest stages of shift in signature is consistent with recycling gin. Subduction-related rocks inboard of Ellesmerian shortening and translation on of Silurian units from the Pearya, Farewell, Pearya are inferred to record transpressional the northern margin coincide with the start northern Alexander, and Arctic Alaska ter- collapse of the Ordovician arc against the of Yukon-Tanana magmatism in the northern ranes (Fig. 2). The εHft values for Ordovician Franklinian margin, with Silurian arc activity Cordillera (Colpron and Nelson, 2009). to Early Devonian grains in many terranes are continuing offshore as subduction migrated markedly juvenile but show a sharp pull down westward. The location of Siberia and its role MESOZOIC TRANSLATION AND in the Late Devonian (Fig. 2), which reflects in the transfer of circum-Arctic terranes to the OPENING OF THE CANADA BASIN increased crustal involvement due to contrac- Cordilleran margin is poorly understood, but Despite lithologic, sedimentologic, and tion and perhaps collision. The Banks Island relative motion between Baltica, Siberia, and structural arguments for translation of Arctic and northern (St. Elias) units of the Alexander the Arctic terranes likely increased after the Alaska along the northern Laurentian mar- terrane (Fig. 1) show a transition from strongly Silurian Baltica–Laurentia collision. Silurian gin (Patrick and McClelland, 1995; Oldow et evolved in Ordovician–Silurian grains to translation placed several crustal fragments al., 1987, 1989; Dickinson, 2009), Early dominantly juvenile values—a signature that and arc terranes along the Arctic margin. Cretaceous counterclockwise rotation of is more consistent with the southern Alexander Silurian to Early Devonian arc activity con- Alaska is the generally accepted model for terrane (Fig. 2). This transition, combined tinued in outboard terranes destined to opening of the Canada Basin (Grantz et al., with the similarity in detrital zircon patterns, approach the Cordilleran realm. 2011). The rotation model persists in large suggests Devonian amalgamation of the dis- Devonian displacement on the CATS part due to a perceived lack of evidence for parate Alexander fragments. emplaced Pearya and the North Slope Mesozoic displacement on the Canadian

www.geosociety.org/gsatoday 7 Arctic margin. Strike-slip faults are clearly Siberia Figure 4. Schematic Mesozoic exposed on Ellesmere Island and record a paleogeographic reconstruction complex history of post-Carboniferous to showing the role of the Canadian SAZ Arctic transform system (CATS) in Eocene sinistral and dextral displacement ESB opening of the Canada Basin and (Piepjohn et al., 2013). These structures Lomonosov Ridge large magnitude extension in the Amerasian Basin. Modified after record reactivation of the Paleozoic trans- PB Patrick and McClelland (1995), Chukotka form margin. West of Ellesmere Island to the AMR MB Dickinson (2009), Miller et al. CBL (2018), and Døssing et al. (2020). Yukon-Alaska mainland, the structural his- SAR AMR—Alpha-Mendelev Ridge; CB TS tory of the Canadian margin is in question. Arctic CA CB—Canada Basin; CBL—Chuk- Alaska Laurentia chi Borderland; ESB—East Sibe- Although conventionally interpreted as rian basins (see Nikishin et al., representative of Mesozoic extension, pub- 2021); MB—Makarov basin; PB— lished seismic reflection profiles across the Podvodnikov basin; SAR—south Amerasia ridge; SAZ—South Anyui northern boundary of the Sverdrup basin suture zone. Extent of thin crust (Embry and Dixon, 1990) show the bound- (<10 km) is from Lebedeva-Ivanova et al. (2019). ary to be disrupted by near-vertical faults Crustal thickness <10 km convergent plate boundary more reasonably interpreted as strike-slip Strike-slip / transform fault normal fault faults. The faults separate blocks with substantial differences in thickness of Late Jurassic and Early Cretaceous sedimentary much more limited extent of oceanic crust displacement along the Arctic margin rocks. The faults cut and are locally sealed (Chian et al., 2016), and interpretation of geo- (Piepjohn et al, 2013) and the Porcupine shear by Late Cretaceous clastic rocks that indi- physical lineaments as transform structures zone marks reactivation of the central and cate displacement into the late Mesozoic. has produced models invoking strike-slip western segments of the CATS, respectively. Along Prince Patrick Island, the faults trun- faults within the Canada Basin (Hutchinson et Activity on the western CATS was linked cate Paleozoic and Mesozoic stratigraphic al., 2017). These new models will be greatly with continued evolution of the Cordilleran and structural trends at a high angle to the improved by incorporating the CATS. In fact, strike-slip orogen (Murphy, 2019). margin (Harrison and Brent, 2005). Local the recent transform model of Døssing et al. evidence of extensional deformation is (2020) explicitly requires sinistral translation CONCLUDING REMARKS described along Banks Island (Fig. 1; Helwig on the Porcupine shear zone. Many uncertain- Available field evidence strongly supports et al., 2011) in a segment of the boundary ties remain regarding the crustal composition the presence of a long-lived strike-slip fault characterized by a slight deflection in strike and the timing and magnitude of extension extending from North Greenland westward to consistent with an extensional step in a within the Canada Basin and broader Alaska along the northern Laurentian margin. sinistral transcurrent fault system (Fig. 4). Amerasian Basin (Lebedeva-Ivanova et al., Onshore and offshore observations are con- Seismic sections west of Banks Island doc- 2019), but tectonic models place the region in sistent with Paleozoic translation of arc ter- ument near-vertical structures that truncate a back arc setting relative to the Mesozoic ranes and crustal fragments along the CATS, the continental margin along the Tuk trans- Cordilleran margin (Miller et al., 2018). followed by Mesozoic reactivation to accom- form (Helwig et al., 2011). Integrating our land-based observations of modate regional extension of continental and The Porcupine shear zone, separated from translation with the offshore geophysics pro- hybrid crust (Miller et al., 2018) during trans- the Tuk transform to the east by a series of vides a realistic geodynamic model for the lational opening of the Canada Basin. north-striking Cenozoic faults that record Cretaceous opening of the Canada Basin in Ongoing geochronologic and kinematic stud- east-west contraction and disrupt the simple this setting (Fig. 4). The greater Amerasian ies of fault rocks will provide additional continuation of the CATS, is essential to Basin is best viewed as a domain of large- insight on the magnitude, timing, and direc- translation models for opening of the Canada magnitude extension in response to slab roll- tion of displacement along the length of the Basin. Preliminary structural studies sup- back on the paleo-Pacific margin that is bound boundary. Pre-Devonian terrane translation ported Late Jurassic to Early Cretaceous by strike-slip displacement on the Laurentian complicates restorations based on age or litho- sinistral transpression along the Porcupine and Siberian margins (Miller et al., 2018). logic similarities since many correlations are shear zone (Oldow and Avé Lallemant, Transforms on the Siberian margin and within non-unique. In addition, extension within the 1993). Recent studies have demonstrated that the Canada Basin are commonly accepted as Canada Basin accommodated by transform reactivation of the Porcupine shear zone components of the rotational model (Amato et boundaries on the Canadian and Chukchi involved Jurassic and Cretaceous rocks (von al., 2015; Doré et al., 2016). Sinistral reactiva- Borderland margins does not preclude block Gosen et al., 2019). Although the magnitude tion of the CATS on the Laurentian margin rotation within the basin, leading to hybrid and timing of Mesozoic displacement on the similarly bounds the extensional domain to models (Miller et al., 2018). Porcupine shear zone is not well documented the south. Block rotation of northern Alaska The rotation model for opening of the at present, sinistral translation associated related to opening of the Canada Basin is Canada Basin has long rested on stratigraphic with opening of the Canada Basin is clear. permissible but no longer required. arguments (e.g., Embry, 1990). Early struc- Marine geophysical data have long been Cenozoic reactivation of the CATS is tural analysis recognized translation of units interpreted in support of the rotation model, recorded along its length. Displacement on with different Paleozoic and Mesozoic defor- particularly satellite gravity data that was the de Geer transform during opening of the mation histories (Oldow et al., 1987, 1989), but inferred to represent a spreading center Eurasian Basin records reactivation at the the necessary kinematic and timing con- (McAdoo et al., 2008). New data suggest a eastern end (Doré et al., 2016). Dextral straints were missing, thus allowing the

8 GSA Today | July 2021 rotation model to persist as the consensus ern Caledonian connection for the Alexander Faehnrich, K., McClelland, W.C., Colpron, M., Nutt, model with little supporting structural evi- terrane: Lithosphere, v. 5, p. 163–168, https://doi C.L., Miller, R.S., Trembath, M., and Strauss, J.V., 2021, Pre-Mississippian stratigraphic architecture dence. For instance, no demonstrable increase .org/10.1130/L255.1. Chian, D., Jackson, H.R., Hutchinson, D.R., Shimeld, of the Porcupine Shear Zone, Yukon and Alaska, in shortening along the length of the Brooks J.W., Oakey, G.N., Lebedeva-Ivanova, N., Li, Q., and significance in the evolution of northern Lau- Range or obvious contraction south of the Saltus, R.W., and Mosher, D.C., 2016, Distribu- rentia: Lithosphere (in press). rotation axis in the Mackenzie delta exists to tion of crustal types in Canada Basin, Arctic Gibson, T.M., Faehnrich, K., Busch, J.F., McClelland, support rotation. The rotation model has in Ocean: Tectonophysics, v. 691, p. 8–30, https:// W.C., Schmitz, M.D., and Strauss, J.V., 2021, A detrital zircon test of large-scale terrane displace- essence achieved the status of a Geomyth doi.org/10.1016/j.tecto.2016.01.038. Colpron, M., and Nelson, J.L., 2009, A Palaeozoic ment along the Arctic margin of North America: (Dickinson, 2003) since it is commonly Northwest Passage: Incursion of Caledonian, Geology, v. 49, p. 545–550, https://doi.org/10.1130/ assumed and rarely tested. Future models for Baltican and Siberian terranes into eastern Pan- G48336.1. Mesozoic opening of the Canada Basin will thalassa, and the early evolution of the North Gilotti, J.A., and McClelland, W.C., 2007, Charac- need to merge existing stratigraphic and geo- American Cordillera, in Cawood, P.A., and teristics of and a tectonic model for ultrahigh- pressure metamorphism in the overriding plate of physical observations with the substantial Kröner, A., eds., Earth Accretionary Systems in Space and Time: Geological Society of London the Caledonian orogen: International Geology database that documents the Paleozoic evolu- Special Publication 318, p. 273–307, https://doi Review, v. 49, p. 777–797, https://doi.org/10.2747/ tion and Mesozoic–Cenozoic reactivation of .org/10.1144/SP318.10. 0020-6814.49.9.777. the CATS in order to solve a tectonic problem Colpron, M., McClelland, W.C., and Strauss, J.V., Grantz, A., Hart, P.E., and Childers, V.A., 2011, that has dogged the community for decades. 2019, Detrital zircon U-Pb geochronological and Geology and tectonic development of the Am- Hf isotopic constraints on the geological evolu- erasia and Canada Basins, Arctic Ocean, in tion of North Yukon, in Piepjohn, K., Strauss, Spencer, A.M., Embry, A.F., Gautier, D.L., ACKNOWLEDGMENTS J.V., Reinhardt, L., and McClelland, W.C., eds., Stoupakova, A.V., and Sørensen, K., eds., Arc- This contribution is based on the results of stud- Circum-Arctic Structural Events: Tectonic Evo- tic Petroleum Geology: Geological Society of ies funded by National Science Foundation EAR lution of the Arctic Margins and Trans-Arctic London Memoir 35, p. 771–799, https://doi.org/ grants awarded to McClelland (0948359, 1049368, Links with Adjacent Orogens: Geological Soci- 10.1144/M35.50. 162413, 1947071), Strauss (1624131, 1650152, ety of America Special Paper 541, p. 397–437, Harrison, J.C., and Brent, T.A., 2005, Basins and 1947074), Gilotti (1049433, 1432970, 1650022), https://doi.org/10.1130/2018.2541(19). fold belts of Prince Patrick Island and adjacent Gehrels (0947904), Macdonald (1049463), and the Cox, G.M., Strauss, J.V., Halverson, G.P., Schmitz, areas, Canadian Arctic Islands: Geological Sur- Arizona LaserChron Facility (1032156, 1338583, M., McClelland, W.C., Stevenson, R.S., and Mac- vey of Canada Bulletin 560, 197 p., https://doi 1649254). Additional support for fieldwork was donald, F.A., 2015, Kikiktak Volcanics of Arctic .org/10.4095/220345. provided by the Yukon Geological Survey (YGS) Alaska—Melting of harzburgitic sub-continental Helwig, J., Kumar, N., Emmet, P., and Dinkelman, and Bundesanstalt für Geowissenschaften und lithospheric mantle associated with the Franklin M.G., 2011, Regional seismic interpretation of Rohstoffe (BGR). This is YGS contribution number Large Igneous Province: Lithosphere, v. 7, crustal framework, Canadian Arctic passive 051. Luke Beranek and Erik Lundin provided con- p. 275–295, https://doi.org/10.1130/L435.1. margin, Beaufort Sea, with comments on petro- structive reviews that improved this contribution. 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